This invention relates to a negative working resist composition and lithography used for producing semiconductor elements and the like. More in detail, this invention relates to a resist material and a process for forming a pattern at the time of forming a negative working pattern using as an energy source for light exposure deep ultraviolet light of 300 nm or less, for example, KrF excimer laser light (248.4 nm), electron beams or X-rays.
With recent progress of semiconductor devices with higher density and increased packing density, light sources used for fine working, particularly those used in light exposure apparatuses for photolithography become shorter and shorter. Now, KrF excimer laser light (248.4 nm) is to be studied. But, negative working resist materials suitable for such a wavelength have not been found sufficiently.
For example, when a known resist material comprising an alkali-soluble resin and a bisazide compound is exposed to KrF excimer laser light or deep UV (ultraviolet light), the sensitivity is so low that it cannot be used for deep UV, KrF excimer laser light and electron beams wherein a highly sensitive resist material is required. Recently, after a proposal of a chemically-amplified resist material wherein an acid generated by exposure to light is used as a catalyst so as to reduce the exposure energy (i.e. to increase the sensitivity) [H. Ito, et al: Polym. Eng. Sci., vol. 23, p. 1012 (1983), etc.], various reports have been made. For example, there are proposed resist materials comprising a melamine derivative having a property of crosslinking with polyvinyl phenol in the presence of an acid and a photosensitive compound capable of generating an acid by exposure to light (a photoacid generator) (e.g. Japanese Patent Unexamined Publication Nos. H3-75652 (EP407086), H4-136858, H4-107560, H2-120366, etc.), a resist material comprising polyvinyl phenol and a photoacid generator having an azido group in the molecule (e.g. Japanese Patent Unexamined Publication No. H2-216153), resist materials comprising polyvinyl phenol having a methoxymethyl group or a methylol group in the molecule and a photoacid generator (e.g. Japanese Patent Unexamined Publication No. H2-170165, German Offenlegungsschrift 4025959, etc.). When these resist materials are used, there is obtained a pattern shape with adverse trapezoids as shown in FIG. 2C due to poor light transmittance of the resist materials, or a pattern shape with round surfaces as shown in FIG. 3C due to insufficient crosslinking reaction caused by deactivation of the acid generated by exposure to light on the surface areas. Sometimes, scum is produced on unexposed areas due to adhesion of fragments released from exposed areas depending on resist materials used. Further, there is another problem in that the pattern size remarkably changes with the lapse of time from the exposure to light to development. Thus, there are many problems to be overcome for practical use.
As mentioned above, although the negative working resist materials utilizing the chemical amplification action are more sensitive than known resist materials, they have many problems in that light transmittance at near 248.4 nm is insufficient, the acid generated by exposure to light is easily deactivated, the pattern size is easily changed with the lapse of time, etc., resulting in making these materials difficult for practical use. Therefore, highly sensitive resist materials overcoming these problems have been desired.